There are known various types of push button devices used in the operating portion of various sorts of electronic devices, etc., in one of which a plurality of buttons are coupled with a base plate through flexible arms.
An example of this type of push button devices is indicated in FIG. 6A. A flexible arm 70 is coupled with a base portion 74 at its lower extremity. At the head portion of the flexible arm 70, a button 71 is formed in one body therewith. A working piece 72 mounted on the flexible arm 70 on its rear side between the button 71 and the base portion 74 extends approximately in the horizontal direction. When the button is pushed, the flexible arm 70 is bent so that the working piece 72 is moved in a direction approximately perpendicular to the direction of the push of the button 71 and pushes a switch 75 on the base plate 76 to drive it.
The push button device having this construction has an advantage that the number of parts and the number of mounting steps can be reduced, because it is not necessary to arrange switches which are turned on and off by working pieces in the direction parallel to the push button device and the switches can be mounted directly on the circuit base plate owing to the fact that the direction of the push of the button and the operation direction of the working piece form an angle of about 90.degree..
On the other hand, the number of functions of electronic devices are represented by e.g. audio devices has increased remarkably and there is a tendency that the number of operation buttons increases also in keeping therewith. In many cases, this increased number of operation buttons are arranged in a plurality of stages taking the size of the front panel of the devices and the operability thereof into account. However, when it is tried to realize arrangement of the plurality of stages of buttons in a push button device having the structure described above, several difficulties are confronted.
Firstly, in the case where the push button device has the structure using a flexible arm, there is a drawback that the amount of push for driving the working piece is different for the upper stage (second stage) and the lower stage if the flexible arm for the push buttons in the upper stage is longer in order to arrange them in plural stages. That is, as indicated in FIG. 5 (in the figure, for the sake of simplifying the explanation, only one is indicated for all the flexible arms 62) in order to move the working piece 63 so as to be inclined by the amount indicated in the figure, for a push button of the lower stage for which the flexible arm 62 is short, it is sufficient to push it over a range of P2 while for a push button of the upper stage for which the flexible arm 60 is long, it is necessary to push it over a range of P1. For this reason, if the push buttons are simply arranged in plural stages, the amount of push is different for the push buttons in the upper and the lower stages which gives rise to a drawback that the operability is bad.
Secondly, the flexible arms supporting the push buttons in the upper stages are necessarily longer than the flexible arms supporting the push buttons in the lower stage. Consequently, the working pieces do not protrude from the rear side of the buttons, but they protrude from the rear side of the flexible arms.
Then, since the part .alpha. (FIG. 6B) of the flexible arm between the button 71 and the working piece 72 is also bent by the pushing operation, the most part of the amount of push of the button 71 is absorbed by this part and therefore, unless the button is pushed over a large range, the working piece 72 is not satisfactorily pushed down which gives rise similarly to a drawback that the operability is worsened.
The inventors of this invention know at this time no push button devices of this type having this 2-stage structure. Consequently, they believe that it is not suitable to call the two drawbacks described above "drawbacks of the prior art techniques". However, these drawbacks have been described in the item of the "BACKGROUND OF THE INVENTION", because these are problematical points which they have encountered in the course through which they have reached this invention and indispensable as a premise for explaining the effect of the invention.